The traditional reliability of telecommunication systems that users have come to expect and rely upon is based, in part, on the reliance on redundant equipment and power supplies. Telecommunication switching systems, for example, route tens of thousands of calls per second. The failure of such systems, due to either equipment breakdown or loss of power, is unacceptable, since such failure may result in the discontinuation of millions of telephone calls and a corresponding loss of revenue.
Power plants, such as battery plants, address the power loss problem by providing the system with an energy reserve (e.g., a battery) in the event of the loss of primary power to the system. A battery plant generally operates as follows. The battery plant includes a number of batteries, rectifiers and other power distribution equipment. The primary power is produced by the rectifiers, which convert an AC main voltage into a DC voltage to power the load equipment and to charge the batteries. The primary power may, however, become unavailable due to an AC power outage or the failure of one or more of the rectifiers. In either case, the batteries then provide power to the load. Redundant rectifiers and batteries may be added to the battery plant as needed to increase the availability of the battery plant.
A battery plant that powers telecommunications systems, such as transmission and switching systems in wireless base stations, commonly employs valve-regulated lead-acid (VRLA) batteries as the energy reserve. The batteries are typically connected in strings (battery strings) and coupled directly to the output of the rectifiers to instantly provide power to the load in the event an AC power outage occurs. During normal operation, the batteries are usually maintained in a fully charged state to maximize a duration for which the batteries can provide energy to the load equipment. However, because all the battery strings in battery plants found in the prior art are charged simultaneously and for the same duration, the individual battery strings are typically not charged to their optimum potentials.
The batteries are typically float charged in multiple battery strings, with each battery string having multiple batteries or monoblocks. For example, four 12V monoblocks may be connected in series to form a 48V battery string. The battery strings are coupled across the output of the rectifiers and are charged by drawing current from the output bus of the rectifiers. As the batteries charge, the amount of current drawn from the rectifiers is reduced, until only a small float current, sufficient to keep the batteries fully charged, is drawn. A float voltage may be adjusted based on battery temperature. With multiple battery strings, however, the temperature of the battery strings may be different. However, since the voltage of the rectifiers' output bus is common to all the battery strings, the float voltage of an individual battery string cannot be set at an optimal level.
Furthermore, the prior art methods of determining the individual capacities of each battery remain crude and imprecise. Current battery plants test the capacity of all the battery strings as a whole. Specifically, to determine the charge capacity of a battery string, the controller adjusts the overall battery plant voltage to allow the batteries in the battery string to discharge at a constant and desired current level. During this process the voltage of the battery string may be monitored to assess its capacity.
A problem occurs when multiple battery strings are employed in a single battery plant. In this situation, while the controller can still adjust the battery plant voltage to provide battery discharge at a constant desired current level, it is necessary to assess the capacities of all the battery strings at the same time. A defective battery string may, therefore, not be detectable.
Accordingly, what is needed in the art is a battery management system, and related method, employable with a battery plant having at least one battery string and, in many instances, a plurality of battery strings, that can individually assess and improve the performance of each battery string in the battery plant.